Which quest?
You don't "accidentally" leave a quest, it asks for you to confirm it when you tap "exit"
@Goodlordbird Nahh if you’ve never done it (somehow) then you wouldn’t understand. It’s like an automatic thing you do in the moment, you don’t mean to quit the quest, you just meant to go back to the previous thing… but quit without thinking. I think a lot of people have accidentally done this by now.
Kabam have been really nice about that in the past for me. I left Crucible after completing like 3/4 of the quest. I filed one of them support reports and someone at Kabam was able to put me back to the spot I progressed to. Make a request on the support page.